The present invention relates generally to radiocommunication systems and, more particularly, to techniques and structures for allowing a mobile telephone to quickly establish an uplink and downlink Medium Access Control transaction.
The growth of commercial communication systems and, in particular, the explosive growth of cellular radiotelephone systems worldwide, has compelled system designers to search for ways to increase system capacity and flexibility without reducing communication quality beyond consumer tolerance thresholds. Mobile calls for example, may be routed in a circuit switched fashion, a packet switched fashion, or some hybrid thereof. It has become increasingly desirable to couple and to integrate mobile cellular telephone networks, for instance a GSM network, to Internet protocol (IP) networks for call routing purposes. The routing of voice calls over IP networks is frequently termed xe2x80x9cvoice over IPxe2x80x9d or, more succinctly, VoIP.
Packet-switched technology, which may be connection-oriented (e.g., X.25) or xe2x80x9cconnectionlessxe2x80x9d as in IP, does not require the set-up and tear-down of a physical connection, which is in marked contrast to circuit-switched technology. This reduces the data latency and increases the efficiency of a channel in handling relatively short, bursty, or interactive transactions. A connectionless packet-switched network distributes the routing functions to multiple routing sites, thereby avoiding possible traffic bottlenecks that could occur when using a central switching hub. Data is xe2x80x9cpacketizedxe2x80x9d with the appropriate end-system addressing and then transmitted in independent units along the data path. Intermediate systems, sometimes called xe2x80x9crouters,xe2x80x9d stationed between the communicating end-systems make decisions about the most appropriate route to take on a per packet basis. Routing decisions are based on a number of characteristics, including: least-cost route or cost metric; capacity of the link; number of packets waiting for transmission; security requirements for the link; and intermediate system (node) operational status.
FIG. 1A shows representative architecture used for communicating across an air link that comprises the packet data protocols which provide connectivity between a mobile end system (M-ES), a mobile data base station (MDBS), and a mobile data intermediate system (MD-IS). An exemplary description of the elements in FIG. 1A and an approach for each element when considering alternative RF technologies follows.
The Internet Protocol/Connectionless Network Protocol (IP/CLNP) are network protocols that are connectionless and widely supported throughout the traditional data network community. These protocols are independent of the physical layer and preferably are not modified as the RF technologies change.
The Security Management Protocol (SMP) provides security services across the air link interface. The services furnished include data link confidentiality, M-ES authentication, key management, access control, and algorithm upgradability/replacement. The SMP should remain unchanged when implementing alternative RF technologies.
The Radio Resource Management Protocol (RRMP) provides management and control over the mobile unit""s use of the RF resources. The RRMP and its associated procedures are specific to the AMPS RF infrastructure and require change based on the RF technology implemented.
The Mobile Network Registration Protocol (MNRP) is used in tandem with a Mobile Network Location Protocol (MNLP) to allow proper registration and authentication of the mobile end system. The MNRP should be unchanged when using alternative RF technologies.
The Mobile Data Link Protocol (MDLP) provides efficient data transfer between the MD-IS and the M-ES. The MDLP supports efficient mobile system movement, mobile system power conservation, RF channel resources sharing, and efficient error recovery. The MDLP should be unchanged when using alternative RF technologies.
The Medium Access Control (MAC) protocol and associated procedures control the methodology M-ESs use to manage shared access to the RF channel. This protocol and its functionality is supplied by alternative RF technologies.
Evolving packet data systems which use the aforementioned protocols will likely support two types of RF channels for packet data transmissions: a packet control channel (PCCH) and a packet traffic channel (PTCH). The PCCH may be either a point-to-point or point-to-multipoint channel. It is this channel on which a mobile station camps (i.e., where the mobile reads broadcast and paging information and where the mobile has random access and reserved access opportunities). The PTCH, on the other hand, is a point-to-point, reserved access only, channel. As will be appreciated by those skilled in the art, an RF channel can provide either packet data services or voice services or can simultaneously provide both packet data and voice services.
FIG. 1B illustrates a state diagram for a conventional mobile station operating, for example, in the protocol architecture illustrated in FIG. 1A. Upon activation, a mobile station selects a PCCH on which to camp. If multiple PCCHs exist in a cell, then the mobile station selects one depending, for example, on the mobile station""s identification. For instance, if the least significant bit of the mobile station""s identification is 00, the mobile station will choose one PCCH; if the least significant bit is 01, it will choose another PCCH, etc. By selecting a PCCH in the above-described manner, paging traffic is spread out over the available PCCHs.
Upon a contention-based access from the mobile station, for the transmission of uplink data, or upon receiving mobile termination data from the network, for the transmission of downlink data, the network (via a base station) may direct the mobile station to tune to a specific PTCH for the establishment of a MAC transaction, e.g., a session for packet transmission. Once on a PTCH, the mobile station enters an active mode 101 and the network schedules resources for the specific mobile to complete the MAC transaction in a reserved access mode.
When the mobile has completed the MAC transaction and a configurable inactivity timer, typically residing in the mobile station, expires (generally after 1 second of inactivity), the mobile station leaves the reserved access mode of the PTCH and returns to camp on the original PCCH and eventually enters a sleep-mode 103. When the mobile station is in a sleep-mode, the mobile station conserves battery life by periodically turning off, and then on, the power of its transceiver such that the PCCH is monitored on a periodic, and not constant, basis.
Upon the reception of additional downlink data from the network, if the mobile station has entered a sleep-mode, the base station will page the mobile station at a designated time slot in order to start a downlink MAC transaction. Alternatively, if the mobile station is not in a sleep-mode, i.e., is still active on the PTCH, the base station will start the MAC transaction at the next available reserved time slot.
Certain user services, e.g., VoIP, include sensitive time constraints over the reserved access channel. That is, delays in the transmission and/or receipt of successive packets can have noticeable and undesirable quality of service (QoS) effects, e.g., on voice quality.
For uplink MAC transactions, the delays in between successive packets can be caused by the mobile station having to wait for the next contention based access opportunity scheduled from the base station. The mobile station must also wait for the response of a requested contention based uplink access until it can utilize all of its capabilities. In addition, collisions may occur upon the contention based access opportunities. That is, if multiple mobile stations try to send MAC requests simultaneously, at least one of the mobiles will cease their request and delay until the next contention based opportunity. This cease and delay procure creates an unpredictable variance in the delay for successive MAC transactions.
For conventional downlink MAC transactions, the inactivity timer can force the mobile station to exit active mode 101 and enter sleep-mode 103. If the time since the last uplink or downlink activity occurred exceeds a predetermined value, i.e., the inactivity timer expires, then the mobile station will enter sleep mode and only monitor certain paging time slots in the superframe phase given by its identity. Once the mobile station enters sleep-mode, the delay until a downlink MAC transaction can be established depends on the time until the next paging opportunity. This delay can be partly avoided by increasing the length of the inactivity timer prior to the initiation of sleep mode. While this technique will reduce the delay between successive packets, it will also increase the rate of battery consumption during the times when the mobile station is receiving non-time critical applications. Furthermore, the demands on bandwidth will be increased which may reduce the capacity of the base station.
At the creation of the uplink MAC transaction, the operator can configure the MAC so that most uplink MAC transactions are created as unbounded transactions. That is, more data from the mobile station application can be added to extend the existing transaction. However, once the data from the mobile station transmit buffers has decreased under a predetermined value, the transaction can no longer be extended. For delay sensitive applications, or premium end-users who desire a high QoS, the delay probabilities described above will influence the next uplink data that needs to be sent.
Therefore, there is a need for a system and method which can mitigate the effects of contention based delay for uplink data taking into account the collision probability and variances in delay. In addition, there is a need for a system and method which overcomes the paging delay for downlink data while still providing a reasonable battery preservation technique without sacrificing delay response time.
For other conventional systems, such as a wireless local area network (WLAN), sleep-mode is used in order to minimize battery consumption by the wireless terminal adapter of the mobile station. However, due to long reactivation times for the entrance and termination of the sleep-mode, the use of sleep-mode may introduce unacceptable delays for real-time applications such as VoIP. The delays for the mobile station are mostly due to collision probability while the delays for the network base stations are mostly due to the paging delays, as well as delays for the required signaling over the air interface prior to the entrance and exit of the sleep-mode. Thus, there exists a need to minimize the battery consumption by a mobile station during real-time applications while also minimizing delay response times.
The present invention overcomes the above-identified deficiencies in the art by providing a method and system for reducing the delay of the transmission of packet data including receiving data from a network via a base station and assigning a mobile station to a packet channel having an active mode and a variable fast page mode. Packet data is exchanged in the active mode until a first inactivity timer expires. The base station and mobile station are then switched to a variable fast page mode in which additional packet data can be exchanged, wherein the variable fast page mode has a greater delay between transmission opportunities than the active mode. The variable fast page mode schedules specific time slots which are monitored for the transmission and receipt of successive packets. In addition, the periodicity of future time slots can vary based on the delay between the successive packets. The mobile station remains in variable fast page mode until the expiration of a second inactivity timer or at the reception of a transmission opportunity and subsequent data transfer to or from the mobile station.